1. Field of the Invention
This invention relates to a process for manufacturing an electrothermal transducer for a liquid jet recording head capable of ejecting liquid and forming flying liquid droplets to effect recording.
2. Description of the Prior Art
Liquid ejecting recording methods (ink jet recording methods) have recently attracted attention since the noise generated during recording is negligible and the recording can be made on plain paper.
Among such recording methods, a method disclosed in Japanese Patent Application Laid-open No. 51837/1979 is different from other methods in that the motive force for ejecting liquid droplets is produced by applying thermal energy to liquid. That is, according to such method, a liquid subjected to thermal energy abruptly changes in volume due to the change in state and the force thus produced ejects the liquid from an orifice at the tip of the recording head portion to form flying liquid droplets, which to attach to a receiving member to effect recording.
The recording head portion of a recording apparatus used for the above-mentioned recording method is constituted of an orifice for ejecting liquid, a liquid ejecting portion having a liquid flow path containing, as a part of the constitution, a heat actuating portion which is communicated with the orifice and where thermal energy is applied to the liquid, and an electrothermal transducer as a means for generating thermal energy.
The above-mentioned electrothermal transducer is constituted of a resistive heater layer formed on a support, and a pair of electrodes disposed opposite to each other and connected with the resistive heater layer. The resistive heater layer has a heat generating region (heat generating portion) between the electrodes. The above-mentioned electrothermal transducer is generally provided on a support and a single or plural protective layers are provided on the surface of at least the portion contacting the liquid of the electrothermal transducer, for example, so as to protect chemically or physically the electrothermal transduder from the liquid, prevent short circuits between the electrodes through the liquid, and inhibit electrolytic corrosion caused by current flowing from the electrodes to the liquid. The protective layers may be generally produced by a thin film forming method such as sputtering, CVD, vapor deposition and the like.
However, the above-mentioned protective layers sometimes suffer from a problem that, upon forming, so-called micro-cracks are formed at an edge of the electrode portion and a defect such as a pinhole or the like is liable to form due to an incomplete washing of dust generated upon forming the layer. It is very difficult to form protective layers completely free from such defects, and when such defects are present in the protective layers, the electrodes may shortcircuit through the liquid to cause corrosion and dissolution of the electrodes and resistive heater layer resulting in disconnection of electrothermal transducer over the long term.
The above-mentioned techniques and problems in the techniques will be described below referring to the drawings.
FIG. 1A is a partial plan view in the vicinity of a heat generating portion of a substrate in a typical embodiment of a prior art liquid jet recording head. In FIG. 1A, a protecting layer for covering the surface is omitted for simplification of the explanation. FIG. 1B is a partial cross-sectional view taken along the dot and dash line XY in FIG. 1A. FIG. 2 is provided for explaining the detailed structure of the substrate in FIG. 1 and is an enlarged cross sectional view of the portion encircled with a dotted line A in FIG. 1B.
In FIG. 1A and FIG. 1B, the electrothermal transducer is constituted of a support 1, a resistive heater layer 2 formed on support 1, and electrodes 3 and 3' formed on the resistive heater layer, and a protective layer 4 is provided on the resulting assembly to protect the electrothermal transducer from ink. Resistive heater layer 2, electrodes 3 and 3', and protective layer 4 are provided on support 1 in the order as mentioned above.
Resistive heater layer 2 and electrodes 3 and 3' constituting the above-mentioned electrothemmal transducer are patterned to form a predetermined shape by means of etching or the like, and the portions other than heat generating portion 11 are patterned in the same shape. At heat generating portion 11, an electrode is not formed on resistive heater layer 2 and the resistive heater layer 2 at that portion constitutes the heat generating portion 11.
Protective layer 4 is formed on desired portions including the portions contacting the liquid above the support by means of sputtering, CVD method, vapor deposition or the like, and the resulting protective layer will usually have defects such as a micro-crack 5, a pinhole 7 or the like as shown in FIG. 2. When such defects are present in protective layer 4, the liquid filling the portions above the protective layer penetrates the defects to corrode and dissolve resistive heater layer 2 and electrodes 3 and 3' finally resulting in disconnection. Therefore, another protective layer such as an organic resin layer and the like has been heretofore usually provided on the protective layer 4. An example of a substrate of a liquid jet recording head provided with such an organic resin layer is shown in FIG. 3.
In FIG. 3, an organic resin layer is provided on the substrate having the constitution of FIG. 1, and FIG. 3 corresponds to the partial cross section of FIG. 1B. In FIG. 3, 8 is an organic resin layer which is formed on the whole surface of protective layer 4 except the portion corresponding to heat actuating portion 5 by means of spin coating, vapor deposition, plasma polymerization or the like.
However, such prior art constitution suffers from the following problems. Firstly, organic resin layer 8 contacts the liquid present thereon and therefore, during the long time use, the resin may swell or its adhesion maybe lowered. In addition, if the protective layer 4 is thick, the transfer of the heat energy generated at heat generating portion 11 to the liquid in the vicinity of said portion 11 is hindered so that the quantity of heat to be generated at the heat generating portion 11 should be increased. As a result, the deterioration of resistive heater layer 2 is accelerated. In such a case as above, the time required for heating and cooling at the heat generating portion 11 becomes long, and this works against high speed recording. Further, the temperature at heat generating portion 11 usually reaches about 200.degree. C. so that the resin of organic resin layer 8 maybe subjected to deterioration. Therefore, heretofore an organic resin layer 8 has not been provided at the portion of protecitve layer 4 in the vicinity of heat generating portion 11 and a single layer structure, that is, only the protective layer 4, is present there as shown in FIG. 3. As a result, the organic resin layer 8 is not effective against micro-crack 6 as illustrated in FIG. 2.